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People of Japanese and European descent who have mutant versions of five genes may be at higher risk of developing Parkinson's disease, two large teams of researchers have found.

The two independent studies, published in the latest issue of Nature Genetics, involved a total of more than 25,000 participants, and are the largest studies to date to try to uncover genetic associations behind Parkinson's disease.

A study in Japan looked only at ethnic Japanese while a second study, in the US, focused only on people of European heritage.

In the first study, Dr Tatsushi Toda of Japan's Kobe University and colleagues sequenced the genes of 2,011 participants with the disease and 18,381 others without the disease.

They found that those with the disease had variants of the genes PARK16, BST1, SNCA and LRRK2.

In the second study, researchers led by Dr Andrew Singleton at the National Institutes of Health's (NIH) laboratory of neurogenetics in the US analysed the genes of more than 5,000 patients of European ancestry who suffer from the disease and detected strong links between Parkinson's and variants of the genes SNCA and MAPT.

The two teams later compared their data and found that variants of PARK16, SNCA and LRRK2 carry risk of Parkinson's in both Japanese and European populations, while variants of BST1 and MAPT were population-specific.

"Because previous Parkinson's genome-wide association studies were too small and lacked power, we worked together to compile and analyse the large data sets needed to identify the elusive genetic variations that play a role in this complex disease," says Singleton.

Parkinson's is a neurodegenerative disease that affects one to 2% of people over the age of 65. It is characterised by tremors, sluggish movement, muscle stiffness, and difficulty with balance.

Although medical treatments may improve symptoms, there are none that can slow down or halt the progression of the disease.

"With this better understanding of the underlying genetic variants involved in the progress of this disorder, we have more insight into the causes and underlying biology of this disease," says Singleton.

"We hope this new understanding will one day provide us with strategies to delay, or even prevent, the development of Parkinson's disease."